SAR Interferometry Capabilities of Canada's planned SAR Satellite Constellation
Dirk Geudtner(1) , Guy Séguin(1)
, and Ralph Girard(1)
Canadian Space Agency,
6767, route de l' Aeroport,
Saint-Hubert (Quebec), J3Y 8Y9,
The Canadian Space Agency (CSA) has initiated the development of a low-cost
small-satellite C-band SAR constellation as a follow-on project to the
RADARSAT-2 program. The low-cost concept requires that the SAR system
design is in terms of mass, power consumption, volume, and antenna size, in
compliance with the constrains set by using a low-cost launch vehicle and a
small satellite bus.
The presentation will provide an overview of the overall mission concept
with a special focus on the SAR interferometry (InSAR) capabilities of the
planned SAR constellation.
The current concept for the SAR constellation involves three satellites
with an option of flying up to six satellites. This is to meet specific
revisit and coverage requirements for ship detection and maritime
surveillance such as oil spill monitoring. Other key applications
envisaged for the constellation will focus on sea ice monitoring, flood
mapping, and InSAR coherent change detection (CCD) of land surfaces for
geohazards and environmental monitoring.
The SAR satellites will operate in two principle modes: a wide-area ScanSAR
and a high-resolution strip-map mode. The wide-area ScanSAR mode with a
swath width of 350 km and a 4-look medium resolution of 50 m will be used
specifically for maritime surveillance and sea ice monitoring. The high-
resolution mode with a 1-look spatial resolution of 5 m is intended for
specific on-demand imagery acquisitions.
The configuration of the constellation is such that the satellites fly at
an altitude of 600 km in the same orbital plane, following each other with
a time separation of about 30 min and 15 min, respectively, depending on
the number of satellites in the constellation (i.e., three or six
satellites). Thereby, the ground track of each satellite is slightly
shifted due to the Earth rotation, providing combined ground coverage of up
to 1000 km using the wide-area ScanSAR mode.
The preliminary configuration concept envisages a 12-day repeat orbit cycle
for each satellite with the goal to maintain its orbit within an orbital
tube of 100 m with respect to other satellites in the constellation.
This is especially interesting for InSAR applications, because for a three-
satellite constellation it means that after 4 days, one of the satellites
will be nearly at the same orbital position as the previous one, covering
the same area on the ground. Provided that the same SAR beam mode is
selected, it will enable the formation of repeat-pass interferometric data
pairs with a 4-day interval.
To enable long-term InSAR measurements, it will be necessary that the
constellation as a whole will maintain its orbit with respect to a
reference orbit within a tight tolerance to ensure the availability of
suitable interferometric baselines (i.e., below half the critical
For wide-area surface change detection applications such as mapping of
crustal deformations and ice motion, an interferometric capable ScanSAR
beam mode will be used. For high-resolution InSAR applications such as
land slide monitoring and glacier motion, the strip-map beam mode will be